Dynasonics DDFXD Doppler Ultrasonic Flow Meter - Manual (Page 9)

06-DPP-UM-00147 02/12 9
PART 1 - INTRODUCTION
GENERAL
The DFX ultrasonic flow meter is designed to measure volumetric flow of solids-bearing or aerated liquid
within closed conduit. Transducers are available as non-contacting (DT9) or insertion probe (DP7) types.
DT9 non-contacting transducers are strapped to the outside of a pipe and are suitable for most instal-
lations where the pipe material supports the transmission of ultrasound. Some pipe materials, such as
concrete pressure pipe and some plastic lined pipes do not allow ultrasound to penetrate to the liquid
inside. For these applications, the DP7 insertion probe will be needed.
The flow meter operates by transmitting an ultrasonic sound from its transmitting transducer through
the pipe wall or from the probe tip into the moving liquid. The sound will be reflected by useful sonic
reflectors
1 suspended within the liquid and recorded by the receiving transducer. If the sonic reflectors
are moving within the sound transmission path, sound waves will be reflected at a frequency shifted
(Doppler frequency) from the transmitted frequency. The shift in frequency will be directly related to
the speed of the moving particle or bubble. This shift in frequency is interpreted by the instrument and
converted to various user defined measuring units.
1 What makes a good Doppler reflector? The four criteria are:
t The scattering material must have a sonic impedance (sound speed difference) at least 10% different
from the fluid.
t There must be some particles large enough to cause longitudinal reflection – particles larger than 35
micron.
t For a given pipe size, the longitudinal reflection must have sufficient energy to overcome the
Rayleigh (energy wasting) scattering caused by smaller particles.
t The reflecting material must travel at the same velocity as the fluid for good accuracy.
APPLICATION VERSATILITY
The DFX flow meter can be successfully applied on a wide range of metering applications. The easy to
program transmitter allows the standard product to be used on pipe sizes ranging from 1” - 120” (25 mm
- 3050 mm) pipe I.D. With the small pipe transducer option, the pipe size range is 0.25” - 1” (6 mm - 25
mm). A variety of liquid applications can be accommodated:
sewage river water
plant effluent mining slurries
sludge others
Because the transducers are non-contacting and have no moving parts, the flow meter is not affected
by system pressure, fouling or wear. Standard transducers are rated to a pipe surface temperature of 250
°F (121 °C). Optional high temperature transducers are rated to operate to a pipe surface temperature of
400 °F (204 °C).